Method of making a microporous material

Abstract

A method for producing a microporous material comprising the steps of: providing an ultrahigh molecular weight polyethylene (UHMWPE); providing a filler; providing a processing plasticizer; adding the filler to the UHMWPE in a mixture being in the range of from about 1:9 to about 15:1 filler to UHMWPE by weight; adding the processing plasticizer to the mixture; extruding the mixture to form a sheet from the mixture; calendering the sheet; extracting the processing plasticizer from the sheet to produce a matrix comprising UHMWPE and the filler distributed throughout the matrix; stretching the microporous material in at least one direction to a stretch ratio of at least about 1.5 to produce a stretched microporous matrix; and subsequently calendering the stretched microporous matrix to produce a microporous material which exhibits improved physical and dimensional stability properties over the stretched microporous matrix.

1. A method for producing a microporous material comprising the steps of:
 mixing ultra high molecular weight polyethylene (UHMWPE), filler and processing plasticizer together to form a mixture, having a weight ratio of filler to UHMWPE of from 1:9 to 15:1 by weight; 
 extruding said mixture to form a sheet; 
 calendering said sheet; 
 extracting all or part of said processing plasticizer from said sheet to produce a matrix comprising UHMWPE and said particulate filler, the filler being distributed throughout said matrix, to produce a microporous matrix sheet; 
 stretching said microporous matrix sheet in at least one stretching direction to a stretch ratio of at least about1.5 to produce a stretched microporous matrix sheet; and 
 calendering said stretched microporous matrix sheet. 
 
     
     
       2. The method for producing a microporous material having improved physical and dimensional stability properties according to  claim 1  where said processing plasticizer is substantially removed from said sheet in the extracting step, with an organic extraction liquid which is a good solvent for said processing plasticizer, a poor solvent for the polymer, and more volatile than said processing plasticizer; where any residual organic extraction liquid is substantially removed by: heat; steam; and/or water; and where any residual water and remaining residual organic extraction liquid are substantially removed by drying prior to stretching said microporous matrix. 
     
     
       3. The method for producing a microporous material according to  claim 1  where said filler is selected from the group consisting essentially of: silica, mica, montmorillonite, kaolinite, asbestos, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, cement, calcium silicate, clay, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gels, glass particles, carbon black, activated carbon, carbon fibers, charcoal, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, lead oxide, tungsten, antimony oxide, zirconia, magnesia, alumina, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, and magnesium carbonate. 
     
     
       4. The method for producing a microporous material according to  claim 3  where said filler is selected from the group consisting essentially of: silica, precipitated silica, silica gel, fumed silica, mica, talc, diatomaceous earth, carbon black, activated carbons, carbon fibers, titanium oxide and calcium carbonate. 
     
     
       5. The method for producing a microporous material according to  claim 1  where said microporous matrix sheet is stretched biaxially which has a stretch ratio in both stretching directions of at least about 1.5. 
     
     
       6. The method for producing a microporous material according to  claim 5  where said processing plasticizer is substantially removed from said sheet in the extracting step, with an organic extraction liquid which is a good solvent for said processing plasticizer, a poor solvent for the polymer, and more volatile than said processing plasticizer; where any residual organic extraction liquid is substantially removed by: heat; steam; and/or water; and where any residual water and remaining residual organic extraction liquid are substantially removed by drying prior to stretching said microporous matrix. 
     
     
       7. The method for producing a microporous material according to  claim 1  where said UHMWPE is mixed with a high density (HD) polyethylene to produce a polyolefin mixture, where said polyolefin mixture has at least 50% UHMWPE by weight of said polyolefin mixture; where said filler to said polyolefin mixture is in a range of from 1:9 to 15:1 filler to polyolefin mixture by weight and where said matrix comprises UHMWPE and HD polyethylene and said particulate filler distributed throughout said matrix. 
     
     
       8. A method for producing a microporous material comprising the steps of:
 mixing ultra high molecular weight polyethylene (UHMWPE), filler and processing plasticizer together to form a mixture, having a weight ratio of filler to UHMWPE of from 1:9 to 15:1 by weight; 
 extruding said mixture to form a sheet; 
 calendering said sheet; 
 extracting all or part of said processing plasticizer from said sheet to produce a matrix comprising UHMWPE and said particulate filler, the filler being distributed throughout said matrix, to produce a microporous matrix sheet; 
 stretching said microporous matrix sheet in at least one stretching direction to a stretch ratio of at least about1.5 to produce a stretched microporous matrix sheet; and 
 calendering said stretched microporous matrix sheet; 
 wherein said microporous matrix sheet having a thickness of no greater than 53.3 microns and a tensile strength in the machine direction of at least 72.9 N/mm 2 . 
 
     
     
       9. The method for producing a microporous material according to  claim 8  where said filler is selected from the group consisting essentially of: silica, mica, montmorillonite, kaolinite, asbestos, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, cement, calcium silicate, clay, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gels, glass particles, carbon black, activated carbon, carbon fibers, charcoal, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, lead oxide, tungsten, antimony oxide, zirconia, magnesia, alumina, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, and magnesium carbonate. 
     
     
       10. The method for producing a microporous material according to  claim 9  where said filler is selected from the group consisting essentially of: silica, precipitated silica, silica gel, fumed silica, mica, talc, diatomaceous earth, carbon black, activated carbons, carbon fibers, titanium oxide and calcium carbonate. 
     
     
       11. The method for producing a microporous material according to  claim 8  where said microporous matrix sheet is stretched biaxially which has a stretch ratio in both stretching directions of at least about 1.5. 
     
     
       12. The method for producing a microporous material according to  claim 8  where said UHMWPE is mixed with a high density (HD) polyethylene to produce a polyolefin mixture, where said polyolefin mixture has at least 50% UHMWPE by weight of said polyolefin mixture; where said filler to said polyolefin mixture is in a range of from 1:9 to 15:1 filler to polyolefin mixture by weight and where said matrix comprises UHMWPE and HD polyethylene and said particulate filler distributed throughout said matrix. 
     
     
       13. A method for producing a microporous material comprising the steps of:
 mixing ultra high molecular weight polyethylene (UHMWPE), filler and processing plasticizer together to form a mixture, having a weight ratio of filler to UHMWPE of from 1:9 to 15:1 by weight; 
 extruding said mixture to form a sheet; 
 calendering said sheet; 
 extracting all or part of said processing plasticizer from said sheet to produce a matrix comprising UHMWPE and said particulate filler, the filler being distributed throughout said matrix, to produce a microporous matrix sheet; 
 stretching said microporous matrix sheet in at least one stretching direction to a stretch ratio of at least about1.5 to produce a stretched microporous matrix sheet; and 
 calendering said stretched microporous matrix sheet; 
 wherein said microporous matrix sheet having a thickness of no greater than 30.5 microns and a tensile strength in the machine direction of at least 47.6 N/mm 2 . 
 
     
     
       14. The method for producing a microporous material according to  claim 13  where said filler is selected from the group consisting essentially of: silica, mica, montmorillonite, kaolinite, asbestos, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, cement, calcium silicate, clay, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gels, glass particles, carbon black, activated carbon, carbon fibers, charcoal, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, lead oxide, tungsten, antimony oxide, zirconia, magnesia, alumina, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, and magnesium carbonate. 
     
     
       15. The method for producing a microporous material according to  claim 13  where said filler is selected from the group consisting essentially of: silica, precipitated silica, silica gel, fumed silica, mica, talc, diatomaceous earth, carbon black, activated carbons, carbon fibers, titanium oxide and calcium carbonate. 
     
     
       16. The method for producing a microporous material according to  claim 13  where said microporous matrix sheet is stretched biaxially which has a stretch ratio in both stretching directions of at least about 1.5. 
     
     
       17. The method for producing a microporous material according to  claim 13  where said UHMWPE is mixed with a high density (HD) polyethylene to produce a polyolefin mixture, where said polyolefin mixture has at least 50% UHMWPE by weight of said polyolefin mixture; where said filler to said polyolefin mixture is in a range of from 1:9 to 15:1 filler to polyolefin mixture by weight and where said matrix comprises UHMWPE and HD polyethylene and said particulate filler distributed throughout said matrix.